Duchenne muscular dystrophy (DMD) occurs in about 1 of 3,000 to 4,000 boys. Laboratory evidence of the disease, notably elevated creatinephosphokinase (CPK), is present already in the newborn infant. Unspecific CPK elevation occurs in the newborn as well, yet disappears shortly thereafter, while in DMD patients the CPK remains high throughout infancy. A new method to reliably determine CPK in a drop of dried blood is described. The method fulfills the criteria given for a suitable screening method in the newborn infant. Although DMD is an incurable disease, early diagnosis has benefits. The latter include early beginning of supportive treatment and particularly recognition of heterozygous carriers of the mutant gene before other affected children are born in a stricken family. It is proposed to adopt the method as a new screening procedure for male newborn infants.